Covid 19 is a new strain, so what? There are new strains of viruses mutating all the time. Hence why you never get immunity to the common cold and influenza.
In normal years, the common cold and influenza are mutation of an existing virus strain found in humans. Typically in pandemic years, a new strain of virus comes from another species such as bats. Current research has identified bats as the host for COVID-19, there is a ~94% DNA match between the viruses. How the human immune system works is well past my education and knowledge, you need to do your own research.
Viruses such as the common cold will evolve over time to a less lethal form. Highly deadly viruses which quickly kill the host tend to die off, dead people rarely infect others.
For your other questions, I will not do your homework for you, it is a complete waste of my time. If you want to learn, go to web sites such as nature.com instead of tin foil hat sites like bitchute.
Freedom of speech does not mean that every web site is obligated to publish your opinions. If you want to get published on Nature.com, collect the evidence to support your ideas by doing the research, use the peer review process to confirm your findings and you may get published by well a respected journal.